Reconfigurable microfluidic device and method of manufacturing the same

ABSTRACT

A microfluidic device, including a substrate including a microchannel, an activation setup disposed in the microchannel, and a matrix array of controllable shape-changing micropillars connected to the activation setup. A shape of the controllable shape-changing micropillars changes based on an activation of the activation setup.

BACKGROUND

The present invention relates generally to a microfluidic device, andmore particularly, but not by way of limitation, to a microfluidicdevice including a microfluidic channel that is dynamically andreversibly changeable during the microfluidic chip operation.

Conventionally, devices that manipulate fluids in the microscale andnanoscale offer benefits to be used as miniaturized laboratories such aslow energy consumption, shorter chemical reaction time, small sample andbiological reagents consumption, low cost, high compactness, highintegration and the possibility of multiple tests per device. Also,microfluidic-based devices may facilitate remote and touch-lessmanipulation of single cells, micro-organisms or micro-particles. Commonmaterials used as microfludic chip substrate are silicon, glass orthermoplastic polymers such as polydimethylsiloxane (PDMS) or polymethylmethacrylate (PMMA). Standard semiconductor fabrication technology(photolithography, dry and wet etching, chemical vapor deposition, etc.)is commonly employed to manufacture microfluidic chips on silicon orglass, while methods such as injection molding or hot embossing areemployed with thermoplastics.

One common aspect of these fabrication methods is that, once amicrofluidic device is built, its characteristics are usually fixed andcan no longer be changed. The microchannel layout, dimensions and otherchannel features such as the presence or absence of obstacles, pillarsor surface grooves cannot be modified during chip utilization. That is,once built, the microfluidic device is generally limited to be used onthe application for which it was originally designed.

One example where this results in a limitation is for microfluidicstructures known as “capillary pumps”, usually comprised of a wideningstructure within the microchannel filled with an array of pillars thatis capable of pulling fluid along the channel by means of capillarypressure. In such structures, the flow rate and volume of fluid thisstructure can remove depends strongly on its geometry, width, size andplacement of the pillars, which are fixed by design and cannot bechanged once built.

Some microfluidic devices, on the other hand, have considered using athermorheological solution that forms a gel on heating such that, byselectively using dynamic photomasking, it results in locally gelledregions that act as channel walls. However, these devices require aliquid solution flowing or contained within a microfluidic chamber,which are hard to control in their liquid states and prone to mix withthe fluid intended for analysis, and require expensive optical equipmentand a photomask to be designed and built every time a change is intendedfor the microchannels.

SUMMARY

In an exemplary embodiment, the present invention can provide amicrofluidic device, including a substrate including a microchannel, anactivation setup disposed in the microchannel, and a matrix array ofcontrollable shape-changing micropillars connected to the activationsetup. A shape of the controllable shape-changing micropillars changesbased on an activation of the activation setup.

In another exemplary embodiment, the present invention can provide amicrofluidic device, including a microchannel, a plurality of activationsetups disposed in the microchannel, and a plurality of groups ofcontrollable shape-changing micropillars, each group of the controllableshape-changing micropillars being connected to a different activationsetup of the plurality of activation setups.

In a further exemplary embodiment, the present invention can provide amethod of manufacturing a microfluidic device, the method includingproviding a substrate including a microchannel, depositing an activationsetup within the microchannel, and connecting an array of controllableshape-changing micropillars to the activation setup such that a shape ofthe controllable shape-changing micropillars is selectively changed byactivating the activation setup.

Other details and embodiments of the invention will be described below,so that the present contribution to the art can be better appreciated.Nonetheless, the invention is not limited in its application to suchdetails, phraseology, terminology, illustrations and/or arrangements setforth in the description or shown in the drawings. Rather, the inventionis capable of embodiments in addition to those described and of beingpracticed and carried out in various ways and should not be regarded aslimiting.

As such, those skilled in the art will appreciate that the conceptionupon which this disclosure is based may readily be utilized as a basisfor the designing of other structures, methods and systems for carryingout the several purposes of the present invention. It is important,therefore, that the claims be regarded as including such equivalentconstructions insofar as they do not depart from the spirit and scope ofthe present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the invention will be better understood from the followingdetailed description of the exemplary embodiments of the invention withreference to the drawings, in which:

FIG. 1 is a perspective view of one example of a microfluidic device 10;

FIG. 2 is a vertical cross-sectional view A-A showing one example of aconfiguration of the microfluidic device 10;

FIG. 3A is a perspective view of an example of electrical connections ofthe microfluidic device 10;

FIG. 3B is an exemplary configuration of the electrical circuitry of themicrofluidic device 10;

FIGS. 4A-4B are an exemplary configuration of the microfluidic device 10according to one exemplary embodiment;

FIG. 5 is an exemplary configuration of the microfluidic deviceaccording to another exemplary embodiment;

FIGS. 6A-6B exemplary depict an embodiment of the invention includingpiezoelectric ceramic micropillars 60;

FIG. 7 depicts a block/flow diagram of a fluid manipulation processaccording to an embodiment of the disclosure; and

FIGS. 8A-8C exemplarily depicts a reconfigurable rock-on-chip designusing the micropillars 60 a of the microfluidic device 10.

DETAILED DESCRIPTION

The invention will now be described with reference to FIG. 1-8C, inwhich like reference numerals refer to like parts throughout. It isemphasized that, according to common practice, the various features ofthe drawing are not necessarily to scale. On the contrary, thedimensions of the various features can be arbitrarily expanded orreduced for clarity.

With reference now to the example depicted in FIG. 1, a microfluidicdevice 10 includes a substrate 20 and a microchannel 50 in which liquidcan flow in the direction depicted in FIG. 1. An electrode array 30including contacts 40 for electrically connecting the electrode array 30are disposed in the microchannel 50. A hydrogel micropillar matrix 60including a plurality of micropillars 60 a (as depicted in FIG. 2 whichdepicts a cross-sectional view A-A of FIG. 1).

That is, a two-dimensional array of polymer micropillars 60 a arrangedin an N×M matrix is integrated inside the microchannel 50.

As shown in FIG. 2, in one possible implementation, the electrode array30 includes a row selection metal line 80, a column selection metal line90, and an electrode or heating element 100 associated with each of themicropillars 60 a. The fluid flow channel 70 is the region between andaround the micropillars 60 a for the fluid to flow in the flow direction(as shown in FIG. 1).

As shown in FIG. 3A, the electrode or heating element 100 (e.g.,activation setup) is disposed between the row selection metal line 80and the column selection metal line 90 such that the electrode orheating element 100 can be attached to a controlled power source tocause the electrode or heating element 100 to activate (or de-activate)to change the dimensions of the micropillars 60 a. High Z means “openelectrical connection” or, a high electrical impedance state. Eachelectrode has three distinctive states (Positive voltage, Ground or HighZ), so that voltages can be applied individually on each pillar. Thatis, the micropillar array 60 of an M×N array is electrically configuredwith the electrical schematic such as depicted in FIG. 3B so that theelectrode or heating element 100 may be activated to configure (orre-configure) a shape of the micropillar array 60. Thereby, eachelectrode or heating element 100 can be set in an “on” state in whichthe electrode or heating element 100 emits heat (i.e., resistive heatgenerated by an electrical current) to cause the micropillar 60 a toreduce a height thereof or in an “off” state to cause the micropillar 60a to return to its original shape as shown in FIG. 2.

FIG. 3B exemplarily shows one possible control scheme of aninterconnection array, which uses a tri-state voltage polarizationscheme (positive voltage, ground and high impedance—High Z) and anindividual state storage memory that allows persistence of individual(and selective) size of the micropillars 60 a.

In an alternative implementation scheme, a two-dimensional array ofelectrodes 100 can be used where the electrical contact between theelectrode 100 and the power source is done using vertical electricalvias through the microfluidic chip substrate. Alternatively, when theelectrode density allows, the electrical contact between each electrode100 and the power source can be done in-plane on the chip surface.Moreover, CMOS (Complementary metal-oxide-semiconductor) technology canbe employed where each electrode 100 in the two-dimensional array isaddressed electrically by the corresponding CMOS element in a CMOSarray. Also, a hybrid of the approaches can be used. Alternatively, anarray of square electrodes

As shown in FIG. 2, each micropillar 60 a in the hydrogel micropillarmatrix 60 can include a corresponding electrode 100 for changing theshape of the individual micropillar 60 a. However, the invention is notlimited to a one-to-one configuration of electrode 100 to micropillar 60a. That is, a predetermined array of micropillars 60 a can correspond toone electrode 100 (e.g., a plurality of micropillars-to-one electrode).In another embodiment, the micropillars 60 a can be arranged tocorrespond to the electrodes in a predetermined shape such thatactivating an electrode to the “on” state causes the micropillar array60 to be configured in the predetermined shape. In other words, themicropillars 60 may be arranged in the microchannel 50 where eachmicropillar 60 a can be individually addressed (or as a group orplurality of micropillars) and a height of the micropillars 60 a iscontrolled such that the geometry of the microchannel 50 can be modifieddynamically and reversibly during the microfluidic chip operation by useof the electrode 100. Thus, a system including a two-dimensional arrayof micropillars 60 a arranged and aligned above a corresponding array ofelectrodes 100 is provided.

For example, a plurality of groups of controllable shape-changingmicropillars 60 a can be connected to the activation setup (e.g.,heater) 100 such that the group of controllable shape-changingmicropillars 60 a changes shape when the corresponding activation setupis activated. It is noted that a plurality of activation setups can beprovided corresponding to different groups of controllableshape-changing micropillars 60 a.

Thus, by controlling the electric field or the temperature gradient inthe micropillars 60 a, a size (i.e., the height) of the micropillar 60 acan be selectively changed. This provides an extremely flexible andadaptive microfluidics structure, suitable for trapping and sortingmicroparticles, mixing fluids, flow control, etc.

In some embodiments, the micropillars 60 are based on either athermoresponsive hydrogel or an electroactive polymer that can changesize in response to a temperature gradient or an applied electric field,respectively. The electrode 100 acts on the micropillars 60 such thatthe geometry (i.e., height) of the micropillars 60 is selectivelychanged, which can affect the flow of the particles suspended in thefluid as well as the fluid flow characteristics themselves.

It is noted that the material of the micropillars is not limited to theabove. The material of the micropillars 60 can include, for example,thermoresponsive hydrogel polymer, dielectric elastomers, apiezoelectric ceramic, etc. That is, the micropillars 60 include asuitable controllable shape-changing material.

For example, temperature-controlled micropillars 60 (i.e., via theheater electrode or element 100) can be made of a thermoresponsivehydrogel polymer such as poly(N-isopropylacrylamide). That is, thehydrogel requires an aqueous medium during growth and the flowing fluidhelps maintain a stable base temperature. When the thermoresponsivehydrogel polymer is heated above a critical temperature, it releaseswater, and then the micropillars shrunk (i.e, the height decreases). Inone embodiment, the micropillar aspect ratio (H/D) is less than one.This may increase robustness of the micropillar 60 a.

In other embodiments, electric field-controlled micropillars comprisinga dielectric elastomer such as silicone or acrylic elastomers can beused for the micropillars 60. The electroactive polymer requiresvoltages of the order of 100 V/μm, but are not in contact with the fluidor the particles, minimizing the risk of damaging biological elementsflowing in the fluid.

In some embodiments, voltage controlled micropillars using apiezoelectric ceramic, such as PZT (Lead zirconate titanate) can be usedfor the micropillars 60. As exemplarily shown in FIGS. 6A and 6B, usageof a piezoelectric ceramic, such as PZT (Lead zirconate titanate), canallow careful control of pillar height or channel segment height.Applying carefully controlled voltages between the metal contacts 61allows control of the piezoelectric ceramic micropillars height 60.

It is noted that the heating element 100 as seen in FIG. 3A can becomposed of a triple layer structure, the layers may comprise aluminum,polycristalline silicon, aluminium or a suitable combination ofmetal-electrical resistive material-metal. The metal used in the firstinterconnection layer does not need to be the same metal of the thirdmetal layer (i.e., the first layer can be aluminum and the third layercan be a different metal, such as gold, copper, palladium, etc).

FIG. 4A and FIG. 4B exemplarily depict a first use case of the inventionfor flow control with a tunable channel. In one embodiment, the width ofa portion of the channel is adjusted by activating particular electrodes100 to cause the micropillars to reduce (or increase) height, therebycausing the channel to become wider or narrower, thus inducing changesin the flow speed or even completely blocking the flow. In analternative implementation shown in FIG. 4A and FIG. 4B, the flow ratecan be controlled by the geometry (e.g., shape) of the obstaclescomprising a microfluidic capillary pump (usually in the form ofmicropillars) located on a section of the microchannel. Thus,microfluidic chips with adjustable permeability that can change duringthe same experiment realization for systematic studies can be enabled.For example, the mean distance between pillars of the microchannel 50 isincreased from FIG. 4A to FIG. 4B, thereby to change flow rate byactivating particular electrodes 100 to change the shape of themicropillars 60 a.

FIG. 5 exemplary depicts a second use case of the invention for particlemanipulation and sorting with adjustable obstacles. Without voltage inany of N×M matrix elements, all the micropillars are at maximum height.By applying a voltage in selected pixels from the array, it is possibleto create a new conformation of micropillars for desired applicationsuch as allowing smaller particles to flow through the array whileretaining larger particles. The invention can be used to dynamicallyrecreate and adjust so-called deterministic lateral displacementstructures [Lab Chip, 2007, 7, 1644-1659] where rows of obstaclesslightly shifted laterally allow small particles to follow the laminarflow streams, whereas large particles are continuously forced to changethe laminar flow stream and are thus continuously displaced andseparated from the smaller particles.

A system according to an illustrative embodiment of the disclosure isdepicted in FIG. 7 and includes (1) a passive part and (2) an activepart. Referring now to FIG. 7, a passive part (e.g., the microfluidicdevice 10) according to an embodiment of the disclosure includes asimple or complex fluid 16 flowing in a microchannel 17 including thehydrogel micropillar matrix 60 as exemplarily depicted in FIG. 1. Theflow can be driven by any external force, such as forces generated by amicropipette, a pressure pump, a syringe pump, a capillarypump/pressure, gravity, etc. A complex fluid can be a binary mixture oran emulsion/colloid in which particles, such as solid beads, liquiddroplets, cells, etc., with known properties, including size, chemicalcomposition, morphology, surface functionalization, etc., are dispersedin the continuous, simple fluid phase.

An active part (e.g., the electrode array 30 and control thereof)according to an embodiment of the disclosure includes a controller unit11 that includes both hardware and software, a electrode voltageactuator 12 that drives the activation of each electrode 100 in theelectrode array 30, one or more sensor components 14 as well as othertype of actuators 13 that operate directly on the hydrogel micropillarmatrix 60 and fluid. The controller unit 11 initializes operation of theelectrode voltage actuator 12 and other actuators 13 based on receipt ofan initial best guess 18 of operational parameters of the micropillar 60a of the hydrogel micropillar matrix 60 to change a shape of themicropillars 60 a. The electrode voltage actuator 12 can manipulate theshape of the micropillars 60 a of the hydrogel micropillar matrix 60.Other actuators 13 can affect other characteristics of the microfluidicdevice or the fluid, such as temperature or flow speed. The sensorcomponent(s) measures and/or quantifies the outcome of the manipulation,represented by the values of properties of the fluid or the particles.The hardware element of the controller unit can include devices such asa circuit board with a microprocessor/microcontroller (hereinafterreferred to as a CPU), signal generators and amplifiers to control theoperation of the various actuators, as well as analyze the sensorreadings. The software component can execute an optimization routine todetermine the state of the actuators that best manipulates the fluidbased on the signals from the sensor or sensors. The optimizationroutine can be based on one or more well-known techniques such asgenetic algorithms, or other less known or customized methods, toperform iterative optimization, self-tuning or active control of thepillar distribution by minimizing/maximizing the readings of the sensor.A control-loop can also be employed to adapt the system to furtherchanges in the operation conditions, such as flow rate, temperature,etc.

In some embodiments, as exemplarily depicted in FIGS. 8A-C, thecontrollable shape-changing micropillars 60 a can create “live” designsto allow for the manufacturing of a reconfigurable rock-on-chip layoutthat can be made to mimic different types of porous media. By loadingdifferent pore/throat size distributions and pore connectivity thereconfigurable porous media can be made to represent either a sandstone,carbonate, shale rock, etc. FIG. 8A exemplarily depicts a “Rock Type A”including similar pore sizes, large throat size variability, and lowpore connectivity while FIG. 8B exemplarily depicts a “Rock type B”including large pore size variability, similar throat sizes, and highpore connectivity.

As shown in FIG. 8C, pore channels in reservoir rocks may range from afew nanometers to tens of micrometers. The base layout of themicropillar array 60 can have appropriate dimensions (diameter D andpitch L) to allow such geometries to be created. The smallest channelwidth a micropillar matrix can generate is given by W=L−D. The particlesize should be, typically, one order of magnitude smaller than theminimum width W, so as not to clog the passage. The typical flow rate inthose devices should be of the order of a few micrometers per second,which represents the scenario in reservoir rocks. That is, by changingthe shape (e.g., height) of the micropillars 60 a, the pore channels inreservoir rocks can be formed.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

Further, Applicant's intent is to encompass the equivalents of all claimelements, and no amendment to any claim of the present applicationshould be construed as a disclaimer of any interest in or right to anequivalent of any element or feature of the amended claim.

What is claimed is:
 1. A microfluidic device, comprising: a substrateincluding a microchannel; an activation setup disposed in themicrochannel; and a matrix array of controllable shape-changingmicropillars connected to the activation setup, wherein a shape of thecontrollable shape-changing micropillars changes based on an activationof the activation setup.
 2. The microfluidic device of claim 1, whereinthe microchannel is configured such that a fluid flows through themicrochannel between the controllable shape-changing micropillars. 3.The microfluidic device of claim 1, wherein the activation setupcomprises an electrode array including: a row selection metal line; acolumn selection metal line; and a plurality of electrodes, eachelectrode of the plurality of electrodes corresponding to each of thecontrollable shape-changing micropillars.
 4. The microfluidic device ofclaim 1, wherein the activation setup comprises an electrode arrayincluding: a row selection metal line; a column selection metal line;and a plurality of electrodes, each electrode of the plurality ofelectrodes corresponding to a group of the controllable shape-changingmicropillars.
 5. The microfluidic device of claim 1, wherein theactivation setup comprises an electrode array including a plurality ofelectrodes, each electrode of the plurality of electrodes correspondingto a group of the controllable shape-changing micropillars.
 6. Themicrofluidic device of claim 1, wherein the activation setup comprisesan electrode array including a plurality of electrodes, each electrodeof the plurality of electrodes corresponding to each of the controllableshape-changing micropillars.
 7. The microfluidic device of claim 1,wherein the contact between the activation setup and the controllableshape-changing micropillars is by heating transfer through thesubstrate.
 8. The microfluidic device of claim 1, wherein thecontrollable shape-changing micropillars comprise a thermoresponsivehydrogel polymer.
 9. The microfluidic device of claim 8, wherein theactivation setup comprises a heat source to activate thethermoresponsive hydrogel polymer by controlling a temperature gradientof the controllable shape-changing micropillars to cause the shape ofthe controllable shape-changing micropillars to change.
 10. Themicrofluidic device of claim 1, wherein the controllable shape-changingmicropillars comprise a dielectric elastomer.
 11. The microfluidicdevice of claim 10, wherein the activation setup comprises an electrodeto electrically activate the dielectric elastomer by controlling anelectrical field of the activation setup to cause the shape of thecontrollable shape-changing micropillars to change.
 12. The microfluidicdevice of claim 1, wherein the activation setup comprises a plurality ofactivation setups corresponding to the controllable shape-changingmicropillars on a one-to-one basis or a one-to-a plurality basis. 13.The microfluidic device of claim 1, wherein the activation setupactivates the controllable shape-changing micropillars by at least oneof electricity and temperature.
 14. The microfluidic device of claim 1,wherein a height of the controllable shape-changing micropillarsincreases or decreases based on the activation setup being in anactivation state.
 15. The microfluidic device of claim 1, wherein theshape of the controllable shape-changing micropillars is reversiblychangeable by activating the activation setup.
 16. The microfluidicdevice of claim 1, wherein the controllable shape-changing micropillarsare arranged and aligned above the activation setup, each activationsetup actuating over each individual controllable shape-changingmicropillar.
 17. The microfluidic device of claim 1, wherein a gap isdisposed between each of the controllable shape-changing micropillars toseparate each controllable shape-changing micropillar from adjacentcontrollable shape-changing micropillars.
 18. A microfluidic device,comprising: a microchannel; a plurality of activation setups disposed inthe microchannel; and a plurality of groups of controllableshape-changing micropillars, each group of the controllableshape-changing micropillars being connected to a different activationsetup of the plurality of activation setups.
 19. The microfluidic deviceof claim 16, wherein a geometric feature of each group of thecontrollable shape-changing micropillars changes based on an activationof the activation setup corresponding to the group of controllableshape-changing micropillars.
 20. A method of manufacturing amicrofluidic device, the method comprising: providing a substrateincluding a microchannel; depositing an activation setup within themicrochannel; and connecting an array of controllable shape-changingmicropillars to the activation setup such that a shape of thecontrollable shape-changing micropillars is selectively changed byactivating the activation setup.